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41.
We have studied the motion of charge carriers along isolated phenylene-vinylene (PV) chains using a combination of experimental and theoretical methods. The conductive properties of positive charges along PV chains in dilute solution were studied by using the pulse-radiolysis time-resolved microwave conductivity (TRMC) technique. This technique enables the measurement of high-frequency (tens of GHz) charge carrier mobilities along isolated PV chains without the use of electrodes. The charge carrier mobility along PV chains with finite and infinite length was studied theoretically by charge transport simulations with parameters from density functional theory (DFT) calculations. The high-frequency charge carrier mobility is found to depend strongly on the conjugation length of the PV chains and is found to increase both with increasing length of the PV chain and with increasing conjugation fraction. The experimental results are in good agreement with the calculated results. On the basis of this combined experimental and theoretical study an intrachain charge carrier mobility of a few tens of cm2/Vs is expected for an infinitely long PV chain without conjugation breaks. 相似文献
42.
Prins P Grozema FC Schins JM Patil S Scherf U Siebbeles LD 《Physical review letters》2006,96(14):146601
We have studied the high-frequency (34 GHz) mobility of positive charge carriers on isolated ladder-type polymer chains in dilute solution. We find that the high-frequency mobility is limited by the chain ends on chains as long as 35 monomers. The intrachain motion of charge carriers can be described by one-dimensional diffusion between infinitely high reflecting barriers, representing the chain ends. Our data indicate that the intrachain mobility for ladder-type polymer chains is close to 600 cm(2)/V s. With this high mobility the ladder-type polymer is a promising candidate for future use as an interconnecting wire in molecular electronics. 相似文献
43.
Roel Prins 《Angewandte Chemie (International ed. in English)》2019,58(43):15548-15552
A non‐spinel model for the structure of γ‐Al2O3, with 25 % of the Al3+ cations at tetrahedral positions, has been the subject of wide interest. However, 17O NMR measurements and, more recently, 27Al NMR measurements have shown that there are considerably more Al3+ cations at tetrahedral positions. This means that the Al3+ vacancies in γ‐Al2O3 are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe2O3 and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al2O3, and thus, for catalysis. 相似文献
44.
Wijnand Hoitinga Roel de Groot Marcel Kwakkel Marc Gerritsma 《Journal of computational physics》2008,227(4):2411-2429
This paper describes an equivalent but improved least-squares formulation for the numerical approximation of the solution of partial differential equations. Instead of using variational analysis to impose the conditions for minimizing the residual, the residuals are minimized directly, thus leading to a method we will denote by Direct Minimization (DM). DM circumvents setting up the normal equations which consists of matrix–matrix multiplications. Matrix–matrix multiplications are expensive, may lead to loss of accuracy and destroy the sparsity pattern present in the original system. The condition number of the DM formulation is the square root of the condition number which would be obtained if variational analysis was employed. An element-by-element procedure will be presented which allows for parallelization of DM. A computational comparison between DM and the conventional least-squares formulation based on variational analysis will be presented. 相似文献
45.
Liu L Van Campenhout J Roelkens G Soref RA Van Thourhout D Rojo-Romeo P Regreny P Seassal C Fédéli JM Baets R 《Optics letters》2008,33(21):2518-2520
A compact electro-optic modulator on silicon-on-insulator is presented. The structure consists of a III-V microdisk cavity heterogeneously integrated on a silicon-on-insulator wire waveguide. By modulating the loss of the active layer included in the cavity through carrier injection, the power of the transmitted light at the resonant wavelength is modulated; approximately 10 dB extinction ratio and 2.73 Gbps dynamic operation are demonstrated without using any special driving techniques. 相似文献
46.
We propose that a boxlike filter response can be obtained by utilizing complementary photonic bandgap properties of the column and row configurations in two-dimensional microresonator arrays. The filters are fabricated using deep-UV lithography in silicon-on-insulator technology. The observed sidelobes reduction is approximately 10 dB, and the usable bandwidth can be as high as 500-750 GHz. 相似文献
47.
Pieter F. W. Stouten Theo G. Prins Albert J. M. Duisenberg Jan A. Kanters Narinder S. Poonia 《Journal of chemical crystallography》1991,21(5):553-557
Na+ [C6H2(NO2)3O]– H2O,M
r=269.11, monoclinic,C2/m (No. 12),a=13.065(1),b=20.065(2),c=3.6957(4) Å,=90.75(1)°,V=968.7(1) Å3,Z=4,D
m=1.848 g cm–3 (by flotation),D
x=1.845 g cm–3, (CuK)=1.54184 Å,(CuK)=17.5 cm–1,F(000)=540,T=295 K,R=0.055,wR=0.060 for 879 observed reflections withI2.5(I). p]In the structure the picrate anion has exact twofold symmetry, the water molecule has exact mirror symmetry and the two sodium cations occupy special positions on inversion centers at (0, 1/2, 0) and (1/2, 1/2, 1/2). The phenyl ring together with the four substituent N and O atoms is strictly planar, but the phenyl ring is severely distorted from hexagonal symmetry, as is commonly observed in structures containing the picrate fragment. Both sodium ions are eight-coordinated with Na(1) and Na(2) in a cubic and distorted cubic arrangement, respectively. Na(1) coordinates to four charged phenoxide O atoms and four O atoms of nitro groups, and Na(2) to four O atoms of nitro groups and four water molecules. The water molecule donates two hydrogen bonds to symmetry-related O(2) atoms ofortho nitro groups. Two symmetry-related O(3) atoms ofortho nitro groups serve as acceptors in a very unusual asymmetric bifurcated C-HO hydrogen bond. 相似文献
48.
49.
Functionalization of multivalent structures such as dendrimers and monolayer passivated nanoparticles with catalytically active groups results in very potent catalysts, a phenomenon described as the positive dendritic effect. Here, we describe a series of peptide dendrons and dendrimers of increasing generation functionalized at the periphery with triazacyclononane, a ligand able to form a strong complex with Zn(II). Kinetic studies show that these metallodendrimers very efficiently catalyze the cleavage of the RNA model compound HPNPP, with dendrimer D32 exhibiting a rate acceleration of around 80,000 (kcat/k(uncat)) operating at a concentration of 600 nM. A theoretical model was developed to explain the positive dendritic effect displayed by multivalent catalysts in general. A detailed analysis of the saturation profile and the Michaelis-Menten parameters kcat and KM shows that it is not necessary to ascribe the positive dendritic effect to, for instance, changes in the catalytic site, increased substrate binding constant, or changes in the microenvironment. Rather it appears that the efficient catalytic behavior of multivalent catalysts is mainly determined by two factors: the number of catalytic sites occupied by substrate molecules under saturation conditions, and the efficiency of the multivalent system to generate catalytic sites in which multiple catalytic units act cooperatively on the substrate. 相似文献
50.
[reaction: see text] The Ti(IV) complex 2c bearing a C3-symmetric triphenolate amine ligand is an air and moisture tolerant complex that efficiently catalyzes sulfoxidation reactions at room temperature without previous activation (catalyst loading down to 0.01%, TONs up to 8000, TOFs up to 1700 h-1, quantitative yields). Reactions were performed with aqueous hydrogen peroxide as oxidant, which adds value to the methodology from the environmental viewpoint. 相似文献